In recent years, resinous optical discs are being used for various purposes such as for music discs, CD-ROM for computers, and cinema discs. A reason for the rapid diffusion is that the memories of such discs are rarely damaged by optical reading.
However, the surface layers covering the memories are made of transparent resin. This resinous surface is easily scratched. Reading errors (eg. sound "jumping" or movement of pictures) are caused by the scratches. In order to eliminate the scratches, it is necessary to polish the surface layer.
In one typical polishing method, a polishing pad, which is used as a polishing material, contacts the surface of a disc which is to be polished (hereinafter referred to as "the surface for polishing"). The diameter of such a polishing pad is the same as the width of surface for polishing. The disc and the polishing pad are simultaneously rotated. An abrasive is poured between the polishing pad and the disc and then the disc is polished.
The above mentioned polishing methods have the following problems.
(1) Irregularities may be caused by the polishing pad which is rotating under a constant condition, since the speed of the inside of a disc is different from the speed of the outside (since the outside is faster than the inside, the inside of a disc is more difficult to polish than the outside).
(2) Static electricity is generated by the friction between the disc and a polishing pad, and then polishing-dust sticks to the surface of the disc.
(3) The disc is overheated by the frictional heat, and the disc is, then, deformed.